Control system



Oct. 4, 1938. w R N 2,132,264

CONTROL SYSTEM Filed Feb. 1, 1936 Fig.1.

JHA/fE/Q MA GA/ET William hing, g 6. M

Hi Attorney.

Patented 0.1.4, 1938 2,132,264

UNITED STATES PATENT OFFICE 2,132,264 ooN'raoL stem William R.,King, Schenectady, N. Y., minorto \General Electric Company, a corporation oi.

New York Application February 1, 1938, Serial No. 61,937 Claims. (01. TIL-240) This invention relates to control systems, more the following specification and to the accompar'ticularly to systems for controlling the actupanying drawing in which Fig. 1 is a simple diaation of reciprocating loads, and it has for an grammatical illustration 01' an embodiment of the object the provision of a simple, reliable, efilcient invention and Fig. 2 is a chart of characteristic 5 and improved system of this character. curves explaining the operation of the invention. 5

More specifically, the invention relates to con- Referring now to the drawing, one terminal of trol systems for vibrating screens and the like in a magnet coil i0, such for example as the shaker which the coil that actuates the load is supplied magnet 01 a vibrating screen, is connected to one with a periodically varying voltage from an elecside of a suitable source of alternating voltage tric valve which in turn is supplied from a source repres n ed by the supp lines An electric of alternating voltage. In most industrial areas valve I3 is interposed in the connections between the frequency of the voltage supply has some the opposite terminal of the magnet coil i0 and fixed value, such for example as sixty cycles. In the side l2 of the supply source. As shown, the the absence of any special control apparatus, a anode lit, of the valve is connected to the side 15 valve energized from such a source would deliver H of the supply source and the cathode lac is 5 sixty current impulses per second to the coil connected through conductors i i and E5 to the which in turn would deliver sixty impulses to opposi e terminal of the magnet oil ill. The the load. For certain applications, it is often devalve is also provided with a control electrode o sirable to cause the coil to deliver a lesser numg d b which serves to Cfmtrol the p a e o her of impulses to the load, such for example as current between the'eathode and the anode. 2G thirty, twenty or fifteen impulses per second. Although the valve i3 may be of any suitable commutator devices and, synchronous switches type, it is preferably of the three or four-elechave previously been utilized for producing low t de type. i the Envelope Of which a Small frequency voltage, but such devices are expensive, quantity of an inert gas such for example as g5 require costly maintenance and in general leave mercury vapor is introduced after exhaust. The 26 much to be desired. Accordingly, a further 0bpresence of this gas within the envelope serves to ject of this invention is the provision of a conconvert the usual pure electronic discharge into trol system of this character for controlling an an arc stream thereby constituting the valve an electric valve to pass the desired low ire uency electrostatically or grid controlled arc rectifier.

3-!) current impulses to the actuating coil and in In valves of this type, current will flow between 39 which the control is carried out entirely by means the anode the electrode during that half of stationary elements and apparatus. cycle of the applied voltage in which the voltage In carrying the invention into effect in one of the anode is positive with respect to the form thereof, an electric valve having an anode, voltage of t cathode, provided the voltage of 3 5' cathode and control electrode is connected behe g d 5 o Positive than a lfilefictelmined tween a source of alternating voltage the critical value necessary to initiate the current actuating coil. An energy storage device, for exflow. Once current has started to how, between ample, a capacitance, is connected across the the anode and cathode, the grid does not readily output circuit of the valve with a connection to control the magnitude of the current flowing in 49 the control electrode. When the valve passes the output circuit. Consequently, the current current to the coil during a positive half cycle of flow in the output circuit can only be stopped by the anode voltage, the capacitance becomes interrupting the anode circuit or reducing the charged and applies a negative voltage to the anode voltage to zero. For the pu pose of supcontrol electrode which maintains the valve nonplying a volta e to h id ufficiently positive conducting. Means are provided for discharging to initiate the flow of current between the anode the energy storage device at a predetermined rate and cathode, a transformer i6 is provided, the so that the valve is again rendered conducting primary winding l6; of which is connected across after an interval of one or more positive halt the supply line ii, 12. This transformer has a cycles, as desired. plurality of secondary windings I61), I60 and its.

50 In illustrating the invention in one form there- One terminal of a capacitance I1 is connected 50 of, it is shown as embodied in a system for conthrough a protective resistance i8 to the grid I31; trolling the actuating coil for a vibrating screen and the opposite terminal of this capacitance is or the like. connected through variable resistance i9 and re- For a better and more complete understanding sistance 20 to the cathode '30- The terminals of of the invention, reference should now be had to the secondary winding its are connected across 55 the capacitance I1 and a resistance 2| connected in series relationship therewith sothat an alternating voltage is introduced into the grid or input circuit of the electric valve I3. Energy for heating the cathode I30 to the required degree of incandescence is supplied from the secondary winding Hid to which the heating filament of the cathode is connected as illustrated.

As thus far described, the electric valve is would become conducting once during each cycle of the alternating voltage of the source ii, I 2 and would pass an impulse of current to the magnet coil Ill once during each cycle. Since it is desired to pass a lesser number of current impulses through the magnet coil than the number of cycles of the voltage of the source, means are provided for rendering the valve non-conducting during one or more subsequent positive half cycles of the applied voltage. To this end, an energy storage device, illustrated as a capacitance 2, is connected from the cathode I36 to the side H of the supply source through a rectifier 23 and a resistor and is also connected to the common connection between the resistance 2| and the capacitance I! which is connected to the grid i3b. Thus, the capacitance 22 is connected from the cathode I3c to the grid I21). When the valve I3 is conducting during a positive half cycle 3? anode voltage, the capacitance 22 becomes charged and applies a negative voltage to the grid l3s so that during the following positive half cycle of anode voltage, the voltage of the grid is maintained more negative than the critical grid voltage. As a result, the valve l3 does not conduct current during the following positive half cycle of anode voltage. In order to render the valve conducting after one or more positive half cycles of anode voltage, as desired, means are provided for discharging the capacitance 22 at a predetermined rate. These means are illustrated as resistances I9, 20 connected in parallel with the capacitance 22.

In order to prevent the discharge of the capacitance 22 by the reverse voltage across the coil ID, the rectifier 23 is included in the connections between the capacitance 22 and the side ll of the supply source. Although the rectifier 23 may be of any suitable type it is preferably a vacuum tube having anodes 23a and a-hot cathode 23b which is heated to the required degree of incandescence by means of energy supplied from the secondary winding is to which the cathode is connected as illustrated.

With the foregoing understanding of the elements and apparatus and their organization in the completed system, the operation of the systern itself will be readily understood from the fol lowing detailed description.

In Fig. 2, the alternating voltage of the source ll, i2 is represented by the sinusoidal curve 24 in which ordinates above the axis 0-0 represent positive values of voltage and ordinates below the axis 0Orepresent negative values of voltage. The voltage supplied to the grid circuit through the secondary winding l6b of the transformer is represented by the light sinusoidal curve 25. Preferably the voltage represented by the curve 25 leads the voltage 24 by an angle determined by the constants of the capacitance I1 and the resistance 2|. However, for the purpose of simplicity, this voltage is shown and described as in phase with the anode voltage. The critical grid voltage of the electric valve I3 is represented by the dotted curve 26. v If the voltage of the grid remains less positive, 1. c. more negaplied to the grid l3.

tive than this critical grid voltage throughout the positive half cycle of anode voltage the valve l3 will not conduct. If at any instance this critical grid voltage is exceeded the valve it will become conducting and will continue to pass current during the remainder of the positive half cycle of applied voltage and as long thereafter as the anode remains positive.

Thus, since the grid voltage of the valve 68 becomes more positive than the critical value at the beginning of the first positive half cycle of the anode voltage 24, the valve l3 becomes conducting and a pulse of current represented by the heavy curve 27 flows through the magnet coil Hi. When the anode voltage 24 passes through zero, the current 2'8 would ordinarily tend to stop flowing, but owing to the inductance of the coil ill the current continues to flow until a time '1; during the negative half cycle of voltage. At this point the current flow through the coil ceases.

As the current through the coil Ill builds up, the capacitance 22 becomes charged with the polarity indicated in the drawing so that a negative voltage represented by the curve 28 is ap-- Now the actual grid voltage is the algebraic sum of the voltage represented by the curve 25 and the voltage represented by the curve 28 and is represented in Fig. 2 by the undulating curve 29. When the capacitor 22 attains its maximum potential, the charge begins to leak oil as represented by the upward slope of the curve 28 at a rate depending upon the ohmicvalue of the resistances i9 and 20.

During the second P sitive half cycle of the anode voltage 24, the actual grid voltage 29 at no time exceeds the critical grid voltage 26 and consequently the valve l3 remains non-conducting during the entire second positive half cycle of anode voltage. However, during the third positive half cycle of anode voltage, the actual grid voltage becomes more positive than the critical grid voltage and consequently the valve I3 again becomes conducting and passes a second impulse of current through the magnet coil l0 and thereafter the previously described operation is repeated. Thus, it will be seen that the valve l3 only becomes conducting during every other positive half cycle of anode voltage and therefore, if the frequency of the voltage of source il, i2 is of some commercial value such for example as sixty.

cycles, the frequency of the current impulses through the coil ill will be thirty impulses per second.

By varying the value of the resistance [9, the rate of discharge of the capacitance 22 can be still further decreased, and the number of current impulses per second still further reduced. In practice, the number of current impulses has been reduced to one impulse for every thirty positive half cycles of anode voltage, although there was no indication that this was the limit.

When the voltage passes through zero at the end of a positive half cycle in which the valve I3 is conducting the voltage across the magnet coil i0 reverses. This voltage reversal would discharge the capacitance 22 if it were not for the rectifier 23 which prevents passage of current in such a direction as to discharge the condenser.

It will sometimes be found advantageous to advance the AC grid voltage represented by the curve 25 a substantial phase angle ahead of the anode voltage in order to insure that the valve l3 will fire as early in the cycle as possible during those positive half cycles of anode voltage in pointed out, this is etiected by means of the pacitance IT in the grid circuit.

It will also sometimes be found advantageous to substitute for transformer secondary winding l6b a secondary winding on a separate transformer of the type commonly known as a peaking transformer. The peaked voltage wave obtained from the secondary of this transformer will further insure that the valve I3 will fire as early in the cycle as possible during those half cycles of anode voltage in which the valve is to conduct.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form, it will be understood that the elements and apparatus are merely illustrative and that the invention is not limited to the exact arrangement shown in the drawing since alterations and modifications will readly suggest themselves to persons skilled in the art without departing from the true scope of the invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A control system for a reciprocating load comprising a coil for operating said load, means for supplying a periodically varying voltage comprising an electric valve connected between a source of periodically varying voltage and said coil, and having an anode, cathode and control grid, means for supplying a voltage more positive than a predetermined critical value to said grid during a positive halt cycle of the voltage of said source thereby to energize said valve to pass current, and means for maintaining the voltage of said grid more negative than said critical value during a succeeding positive half cycle thereby to render said valve non conducting comprising a capacitance connected across said cathode and grid and having aoonnection to one terminal of said coil and a rectifier in said connection for preventing discharge of said capacitance by reversal of voltage of said coil.

2. A control system for reciprocating load comprising a coil for operating the load, means for supplying a periodically varying voltage to said coil comprising an electric valve connected between said coil and a source of voltage of predetermined irequency and having a cathode, anodeand control grid and means for controlling the frequency or the voltage applied to said coil comprising a capacitance connected across said cathode andgrid and having a connection to said coil, airesistance connected in parallel with said capacitance for controlling the rate 01' discharge thereof, and a rectifier included in said connection for preventing discharge of said capacitance by reversal oi. the voltage of said coil.

3. A control system for a reciprocating load comprising a coil for operating said load, means for supplying a periodically varying voltage to said coil comprising an-electric valve having an anode connected to a source of alternating voltage, a cathode connected to one terminal 0! said coil and a control grid, connections from said amazes source to said grid so that the voltage of said grid is more positive than a predetermined critical value during a half cycle when the anode voltage is positive thereby to render said valve conducting, means for controlling the frequency of the voltage supplied to said coil comprising a capacitance connected from said cathode to said grid and having a connection to the other terminal of said coil to maintain the voltage of said grid more negative than said critical value during a succeeding positive half cycle of anode voltage thereby to render said valve non-conducting, and a resistance connected in parallel with said capacitance to control the rate of discharge thereof, and a rectifier in said connection for preventing the discharge of said capacitance by reversal of the voltage of said coil.

4. A control system for a reciprocating load comprising a coil for operating the load, means for supplying a periodically varying voltage to said coil comprising an electric valve having an anode, a cathode and control grid, means for controlling the frequency of said voltage comprising means for supplying an alternating voltage to said grid, an energy storage device connected across said cathode and control electrode and having a connection to one terminal of said coil, and means for advancing the phase relationship of the alternating component of the grid voltage relative to the anode voltage to insure energization of said valve substantially at the beginning of a positive hall cycle of anode voltage.

5. A control system for a reciprocating load comprising a coil for operating the load, a source of alternating voltage of predetermined frequency, means for supplying a periodically varying voltage of reduced frequency to said coil comprising an electric valve having an anode connected to said source, a cathode connected to one terminal or said coil, and a control grid, conections from said source for supplying an alternating voltage to said grid so that the grid voltage is more positive than a predetermined critical value when the anode voltage is positive thereby to energize said valve to conduct current, a capacitance connected from said cathode to said grid and having a connection to'the opposite terminal of said coil for maintaining the voltage oi said grid more negative than said predetermined value during the following positive halt cycle of anode voltage thereby to render said valve nonconducting, a rectifier included in said connection for preventing discharge of said capacitance by reversal of the voltage of said coil. a resist ance connected in parallel with said capacitance for controlling the discharge of said capacitance to render said valve conducting during a subsequent positive halt cycle at anode voltage, and a capacitance included in circuit with said grid for insuring energization of said valve at approximately the beginning of a positive hali cycle 0! said anode voltage.

WILLIAM R. KING. 

